1. Field of the Invention
The present invention relates to a light-sensitive composition suitable for use in making presensitized plates, IC circuits and photomasks and more particularly to a light-sensitive composition comprising a negative-working or positive-working light-sensitive compound and a polymeric compound having an excellent wear resistance.
2. Description of the Prior Art
A light-sensitive composition comprising o-naphthoquinone diazide compound and novolak type phenolic resin, which belongs to the positive-working system, has been known to be a very excellent light-senstive composition and has industrially been employed to produce presensitized plates for use in making lithographic printing plates (hereunder referred to as PS plate(s) for simplicity) and as photoresists.
However, such a light-sensitive composition exhibits various drawbacks to be eliminated because of the inherent properties of the novolak type phenolic resin used. For instance, it has a low adhesion to a substrate and is inferior in the coating properties, and the resultant film is fragile, inferior in wear resistance and has an insufficient printing durability when it is used, as lithographic printing plates and, therefore, the application thereof is limited to a narrow range.
In order to solve these problems associated with the aforementioned light-senstive composition, a variety of polymeric compounds have been examined as binders for such a light-sensitive composition. For example, Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") No. 52-41050 proposes polyhydroxystyrene or hydroxystyrene copolymers as such binders. These polymeric materials surely permit the improvement in film-forming properties of the composition. However, the resultant light-sensitive composition exhibits only a low wear resistance. In addition, Japanese Patent Un-examined Published Application (hereinafter referred to as "J.P. KOKAI") No. 51-34711 proposes, as such a binder, a polymeric compound having, in its molecular structure, structural units of acrylic acid derivatives. However, such a polymeric compound also suffers from disadvantages such that the range of proper conditions for developing such a polymer is narrow and that the wear resistance thereof is also insufficient.
Moreover, examples of known polymers having excellent wear resistance include polyurethane resins, for instance, U.S. Pat. No. 3,660,097 discloses a system comprising a combination of a positive-working diazonium compound and a substantially linear polyurethane resin. However, such a polyurethane resin carries no alkali-soluble group, thus has essentially insufficient solubility in an aqueous alkaline developer and, therefore, makes it very difficult to develop it without remaining films unremoved.
Alternatively, J.P. KOKAI No. 61-20939 discloses a light-sensitive composition in which an anionic polyurethane resin is used. Such an anionic polyurethane resin is water-soluble and thus it essentially differs from the water-insoluble polyurethane resin of the present invention. The anionic polyurethane resin exhibits insufficient solubility in an aqueous coating solvent, since it is water-soluble. In addition, it is less favorable to use in a light-sensitive layer of PS plates because it adversely affects the stability of the diazo compounds.
Most of the compounds used as light-sensitive materials in the negative-working systems are diazonium compounds. Among these, the most commonly used ones are diazo resins represented by a condensate of formaldehyde with p-diazodiphenylamine.
The light-sensitive composition employed to form light-sensitive layers of PS plates and composed of diazo resins are classified into two groups, one of which comprises only diazo resins and free from binders, as disclosed in U.S. Pat. No. 2,714,066; the other of which comprises a binder and a diazo resin as disclosed in U.S. Pat. No. 4,275,138. Recently, most of light-sensitive layers of such a PS plate comprise a polymer consisting of a diazo resin and a binder for imparting high printing durability to the light-sensitive layer.
As such light-sensitive layers, there have been known so-called alkaline-developable type layers, un-exposed areas of which are removed (or developed) with an aqueous alkaline developer and so-called solvent developable type layers, un-exposed areas of which are removed with an organic solvent type developer. Among these, the former attracts much attention from the viewpoint of safety and sanitation of the operators. This solubility behavior mainly depends on the quality of the binder utilized. There are known methods for imparting alkali-developable properties to the binders, for instance, a method comprising copolymerizing monomers having carboxyl group as disclosed in U.S. Pat. No. 4,275,138 cited above; and a method comprising introducing carboxyl groups into the polymer by reacting hydroxyl groups of polyvinyl alcohol with a cyclic acid anhydride such as phthalic anhydride. However, the resultant polymer is inferior in wear resistance because of the inherent structure thereof. Such a PS plate containing such a binder in a light-sensitive layer provides only a lithographic printing plate having low printing durability. On the contrary, polyvinyl acetal provides a tough and high wear resistant film, however, it only provides PS plates which are developable only with an organic solvent type developer.
Alternatively, polyurethane resins are known as polymers having high wear resistance. For instance, U.S. Pat. Nos. 3,660,097 and 4,337,307 disclose a system comprised of a combination of a diazonium compound and a substantially linear polyurethane resin and that composed of a polycondensate of diazonium salt and branched polyurethane resin. However, these polyurethane resins include no alkali-soluble group, thus essentially have insufficient solubility in an aqueous alkaline developer and, therefore, it is quite difficult to carry out development without remaining films. unremoved. Moreover, these polymers do not have sites which cause photoreaction with a diazonium compound used together therewith during exposure to light to effectively cause cross-linking and, therefore, the light-sensitive layer comprising such a polymer cannot form images exhibiting sufficient strength.
On the other hand, many attempts have been directed to the use of photopolymerizable composition as the light-sensitive image-forming layer of negative-working PS plates. For example, U.S. Pat. No. 3,458,311 discloses a basic composition comprising a polymer serving as a binder, a monomer and a photopolymerization initiator; U.S. Pat. No. 3,796,578 discloses a composition comprising a polymer serving as a binder into which unsaturated double bonds are introduced to improve the efficiency of hardening; U.S. Pat. Nos. 3,549,367 and 3,751,259 and U.K. Patent No. 1,388,492 disclose compositions comprising novel photopolymerization initiators. These compositions have been used practically in some applications. However, either of these light-sensitive compositions suffers from drawbacks that the sensitivity thereof it greatly influenced by the surface temperature of the PS plate during imagewise exposure to light and that these compositions strongly undergo polymerization inhibition due to oxygen during the imagewise exposure.